What we did.
When we did the experiment, we made sure that we started the stop clock, at exactly the same time as the acid was poured onto the magnesium. To measure the start of the reaction to the finish of the reaction, we took care to stop the clock at the point the magnesium disappeared which signalled the end of the reaction. While we set up the apparatus we kept the reactants separate so that the reaction did not start prematurely so we had a fair test. We made sure the amount of magnesium we used stayed the same in all the experiments (2cm long) so we had a fair test and so this variable did not play a part.
Results.
My results generally proved my prediction correct.
The first experiment I did was 40ml acid: 0 ml of water. This experiment proved very difficult to record, as it was very quick, all the magnesium had dissolved in 20 seconds. We carried on recording but no more gas was given off so we assume that the reaction had finished, we repeated this experiment to make sure that the results were valid and found that we had very similar results.
In the second experiment we had 20ml acid: and 20ml water this proved a lot easier to record, all the magnesium had dissolved after 90 seconds and we carried on recording but no more gas was given off. This was again repeated and with very similar results. This reaction took a lot longer to finish so proves my prediction that the higher the concentration of acid will make the reaction happen quicker.
In the third experiment I used 30ml acid: and 10ml of water. This reaction was quicker than the second experiment, but took twice as long as the first, this proves my prediction that the higher the concentration the faster the reaction but it disproves my prediction that if you double the concentration you double the time of the reaction. I did repeat this experiment again to validate it and found that I had very similar results once again.
In my final experiment I used 10ml acid: 30 ml of water. This reaction took a very long time to finish, it took 260 second and did not give off much gas. It is a very low concentration of acid so this is why. This again proves my prediction correct that a lower concentration of acid will take longer than a high concentration of acid to break down the magnesium. I repeated the experiment again to validate my results and found again that my results were valid.
40ml acid: 0ml water.
20ml acid: 20ml water.
30ml acid: 10ml water.
10ml acid: 30ml water
Conclusion.
In conclusion to my findings I have found that the higher the concentration of acid the quicker the rate of reaction which proves both my theory and my prediction. What I did not manage to prove in my prediction was that if you double the concentration you halve the reaction time. This was not the case as this did not happen even after I repeated the experiment.
If possible I would have liked more time to conduct the experiment. I would have repeated the experiment a third and perhaps even a fourth time to make absolutely sure that my results were completely valid, although I am quite happy they are. There were two real problems in this experiment that made the test slightly unfair, the first was the judgement of the time to stop the stop clock at the end of the experiment. It was difficult to tell if the magnesium had completely disappeared as it was only judged by human sight. If it was possible I would have liked to do this in a different way. Also when reading off the measurements of gas produced it was quite difficult on the quicker reactions, again I would have liked to do this in a more accurate way.
In all though I am quite sure that we conducted the experiment as accurately as possible under the conditions we were in. It would have been quite difficult to improve our experiment much more under the circumstances.
Evaluation
I found in my investigation there were no anomalous results. I think under the conditions we had that I got the best results possible. If I had a better environment to conduct the experiment I would have liked to have weighed the mass of the magnesium instead of measuring it and also would have liked to measure the concentration of the acid in a more accurate way. I could’ve spent a lot more time doing this investigation if it was available. I would of liked to go on to do more concentrations and to have repeated each experiment perhaps as much as 4 times each. If possible I would also have liked to use an electronic recording devise to record my data as this would have been far more efficient and accurate.
